Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$245.65	6.377%	$261.3151	$261.32	$261.30	$261.30
Purchase #2	$95.85	5.677%	$101.2914	$101.29	$101.30	$101.30
Purchase #3	$52.31	4.304%	$54.5614	$54.56	$54.55	$54.60
Purchase #4	$200.93	8.319%	$217.6454	$217.65	$217.65	$217.60
Purchase #5	$41.30	3.257%	$42.6451	$42.65	$42.65	$42.60
Purchase #6	$41.92	8.789%	$45.6043	$45.60	$45.60	$45.60
Purchase #7	$114.82	10.643%	$127.0403	$127.04	$127.05	$127.00
7 purchase totals =	$792.78		$850.1030	$850.11	$850.10	$850.00